1) Field of the Invention
The field of this invention relates to pipes and more particularly to a coupling for different sections of pipe which are to be connected together in a fluid tight manner without requiring welding, soldering, or other conventional types of permanent securing techniques.
2) Description of the Prior Art
Plastic pipe and metal pipe have long been used for the conveying of fluids such as liquids and gases. These pipes include fittings with these fittings being utilized to connect together aligned different sections of pipe. These fittings must be capable of providing a fluid tight seal over a range of temperatures, pressures and a variety of exterior ambient conditions. Specifically for plastic pipe, a reliable coupling is difficult due to stress causing fatigue, stretching or failure of the plastic pipe that will result in leaking of the coupling from an inadequate seal. Couplings used in plastic pipe must be able to withstand axial stresses such as those caused by temperature induced length variations without a decrease in sealing capabilities. In addition, pipe couplings should be easily connectable by ordinary workers that don't require any special skill in order to install the coupling.
Pipe couplings are currently available in many different configurations. The typical coupling includes a body or connector portion into which an open end of a section of pipe is inserted and fixedly secured within that connector. A retaining nut is movably mounted on another section of the pipe with its open end to then be located within the confines of the connector. The retaining nut is then threaded onto the connector. Included within the connector and encircling the pipe are one or more elastic sealing rings, one or more washers, and a grab ring for longitudinally fixing in position the pipe section that has been inserted within the connector. Tightening of the retaining nut onto the connector forces the grab ring to compress radially inward to grip the wall surface of the pipe and also provide longitudinal pressure against the sealing rings to compress such forming of a fluid tight seal between the exterior wall surface of the pipe and the interior of this coupling. In the past, typical coupling designs included a grab ring that must be initially expanded or radially expanded during insertion of the pipe so as to fit around and grip the pipe. This initial radial expansion makes insertion of the pipe more difficult and creates a locking condition that prevents withdrawal of the pipe except by disassembling of the coupling even though the retaining nut has not been tightened.
The present inventor has acquired prior U.S. Pat. No. 5,466,019 directed to a similar type of pipe coupling. One of the disadvantages of this prior art type of pipe coupling was that it included a substantial number of parts. It would be desirable to eliminate some of those parts. Additionally, this prior art type of pipe coupling included a compressible rubber washer which functioned to exert a biasing force against biting members which functioned to dig into the pipe in order to maintain the desired fluid tight connection between the pipe sections. However, it has been discovered that over a period of time this rubber washer will tend to take a set and lose its biasing force which results in an inferior type of connection. Additionally, the pipe coupling of the aforementioned patent had the further disadvantage in that it required the retaining nut to be tightened onto the connector of the pipe coupling. The retaining nut also supports the pipe section into which the biting members of the pipe coupling are to imbed. This rotation of that retaining nut produced grooves of the biting members into the pipe section rather than merely digging into the pipe section. It would be desirable to find a way to tighten the pipe coupling which eliminated the need for rotation of this retaining nut.